Adult Macracanthorhynchus hirudinaceus (thorny-headed worm) are usually seen in the small intestine. They are 10 cm (males) to 65 cm (females) long, 3–9 mm thick, and slightly pink with a transversely wrinkled outer covering. The anterior end bears a spiny, retractable proboscis or rostellum used for firm attachment to the intestinal wall. The eggs (dark brown, embryonated, with 3 embryonic envelopes, 90–110 × 50–65 μm) are ingested by the grubs of various beetles that serve as intermediate hosts. Pigs become infected by ingesting either grubs or adult beetles, and the infection is thus restricted to outdoor pigs. The prepatent period is 2–3 mo and the female lays ∼260,000 eggs/day for several months.
Signs are not specific; antemortem diagnosis is difficult because the ova do not float reliably in salt solutions and thus should be looked for in the sediment. The site of attachment may have a necrotic center surrounded by a zone of inflammation. These lesions usually can be seen through the serosa. The rostellum may perforate the intestinal wall and cause peritonitis and death.
Levamisole and ivermectin are effective for treatment. Control depends on avoiding use of contaminated hog lots or pastures or by regular removal of feces when pigs are kept in sties or small runs.
Last full review/revision March 2012 by Allan Roepstorff, DSc, PhD, MSc